The present disclosure relates to a backside illuminated image sensor and a method of manufacturing the same.
In general, an image sensor is a semiconductor device that converts an optical image into electrical signals, and may be classified or categorized as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) image sensor (CIS).
The CIS includes unit pixels, each including a photodiode and MOS transistors. The CIS sequentially detects the electrical signals of the unit pixels using a switching method, thereby forming an image. The CIS may be classified into a frontside illuminated image sensor and a backside illuminated image sensor.
The frontside illuminated image sensor may include photodiodes formed in a substrate, transistors formed on a frontside surface of the substrate, wiring layers formed on the frontside surface of the substrate, and a color filter layer and micro lens array formed on the wiring layers.
Meanwhile, the backside illuminated image sensor may have an improved light-receiving efficiency in comparison with the frontside illuminated image sensor. The backside illuminated image sensor may include transistors and wiring layers formed on a frontside surface of a substrate, a light-blocking pattern and an anti-reflective layer formed on a backside surface of the substrate, a passivation layer formed on the light-blocking pattern and the anti-reflective layer, and a color filter layer and a micro lens array formed on the passivation layer.
The light-blocking pattern may be made of tungsten and may be formed by forming a tungsten layer on the anti-reflective layer and patterning the tungsten layer to have openings corresponding to pixel regions of the backside illuminated image sensor. In such case, the light-blocking pattern may have a width increasing toward the backside surface of the substrate. More specifically, because it is relatively difficult to etch the tungsten layer, the tungsten layer may be etched so that side surfaces of the light-blocking pattern have a positive slope, and there is a limit to increase a thickness of the tungsten layer. Thus, the light loss may be increased by the light reflection on the side surfaces of the light-blocking pattern, and the effect of reducing the crosstalk by using the light-blocking pattern is also limited.